A central goal of materials science is to reveal how a material deforms under mechanical stress and how the deformation is related to its microstructure. This goal is best achieved by “seeing” the evolving microstructure when the property is measured quantitatively. Mechanical testing methods have thus evolved over time to test materials at the micro- and nanoscale while observing the changes in the specimen. Recent advances in microtechnology offer a new generation of microscale sensors and actuators that allow in situ studies of both living and nonliving materials in analytical instruments. Such experiments are providing new and fundamental insights on the structure-property relations in materials and revealing remarkable links between the mechanical properties of living cells and their functions. This issue presents five articles that discuss state-of-the-art methodologies for in situ mechanical tests and highlights new findings through the use of these techniques.

This article is devoted to recent progress in the area of in situ electron microscopy (scanning and transmission) and will focus on quantitative aspects of these techniques as applied to the deformation of materials. Selected recent experiments are chosen to illustrate how these techniques have benefited from improvements ranging from sample preparation to digital image acquisition. Known for its ability to capture the underlying phenomena of plastic deformation as they occur, in situ electron microscopy has evolved to a level where fully instrumented micro- and nanomechanical tests can be performed simultaneously.

Scanning probe microscopy (SPM) has undergone rapid advancements since its invention almost three decades ago. Applications have been extended from topographical imaging to the measurement of magnetic fields, frictional forces, electric potentials, capacitance, current flow, piezoelectric response and temperature (to name a few) of inorganic and organic materials, as well as biological entities. Here, we limit our focus to mechanical characterization by taking advantage of the unique imaging and force/displacement sensing capabilities of SPM. This article presents state-of-the-art in situ SPM nanomechanical testing methods spanning (1) probing the mechanical properties of individual one-dimensional nanostructures; (2) mapping local, nanoscale strain fields, fracture, and wear damage of nanostructured heterogeneous materials; and (3) measuring the interfacial strength of nanostructures. The article highlights several novel SPM nanomechanical testing methods, which are expected to lead to further advancements in nanoscale mechanical testing and instrumentation toward the exploration and fundamental understanding of mechanical property size effects in nanomaterials.

Understanding the mechanical properties of materials is crucial for their reliable application as bulk materials as well as in a miniaturized form. The deformation of materials is usually non-uniform and, hence, needs to be characterized on a local level. The following article focuses on the in-Situ determination of mechanical stresses in crystalline materials during deformation. This can be achieved by both diffraction as well as spectroscopical methods, where the elastic strain is the parameter measured, which is subsequently converted into stresses by the application of Hooke's law. As in Situ measurements require rapid data acquisition in conjunction with reasonable penetration depths, we will focus on x-rays. However, the different techniques described can be applied to any other diffraction probe as well. The description of diffraction techniques, which span the range from averaging techniques to 2D and 3D strain mapping, is complemented by a section on Raman spectroscopy as an alternative method for stress determination for non-metallic materials. Local stresses also can be correlated to local defect densities.

Mechanical testing of micro- and nanoscale materials is challenging due to the intricate nature of specimen preparation and handling and the required load and displacement resolution. In addition, in Situ testing requires the entire experimental setup to be drastically miniaturized, because conventional high-resolution microscopes or analytical tools usually have very small chambers. These challenges are increasingly being addressed using microelectromechanical systems (MEMS)-based sensors and actuators. Because of their very small size, MEMS-based experimental setups are the natural choice for materials characterization under virtually all forms of in Situ electron, optical, and probe microscopy. The unique advantage of such in Situ studies is the simultaneous acquisition of qualitative (up to near atomic visualization of microstructures and deformation mechanisms) and quantitative (load, displacement, flaw size) information of fundamental materials behavior. In this article, we provide a state-of-the-art overview of design and fabrication of MEMS-based devices for nanomechanical testing. We also provide a few case studies on thin films, nanowires, and nanotubes, as well as adhesion-friction testing with a focus on in Situ microscopy. We conclude that MEMS devices offer superior choices in handling, actuation, and force and displacement resolutions. Particularly, their tight tolerances and small footprints are difficult to match by off-the-shelf techniques.

The biconcave shape and corresponding deformability of the human red blood cell (RBC) is an essential feature of its biological function. This feature of RBCs can be critically affected by genetic or acquired pathological conditions. In this review, we highlight new dynamic in vitro assays that explore various hereditary blood disorders and parasitic infectious diseases that cause disruption of RBC morphology and mechanics. In particular, recent advances in high-throughput microfluidic devices make it possible to sort/identify healthy and pathological human RBCs with different mechanobiological characteristics.

Egyptian pigments include the most successful synthetic blue pigment made, which has been in use for more than 2500 years. The nature of some Egyptian pigments, such as malachite, azurite, green earth, and calcite are briefly reviewed. The principal artworks examined here are a group of several 26th Dynasty coffins in the collection of the San Diego Museum of Man. This article examines the nature of the wooden substrate, binder, pigments, and alteration products. The conservation needs of the collection are of special importance. The pigments used in the coffins are malachite, orpiment, carbon black, calcite, and red ocher. Gum Arabic was used as a binder. Wood anatomical studies identified fig as the wood. This article also covers the degradation product, oxammite, resulting from the microbiological decay of textile threads on a Hawk Mummy.